Rendering mortars in Medina Azahara .1. Material characterization and alteration process

Rendering mortars, which are still exposed to the open air on some of the walls of Medina Azahara, are studied and characterized in this work. Some repairing mortars used in different previous restorations are also characterized. Those rendering mortars are of different make considering the composition of their binder: lime, gypsum and mixed lime/gypsum. Repairing mortars used in previous interventions are made of lime, excepting for a portland cement used by Felix Hernandez in the restoration of one of the rooms back in the 50's. Biological colonization is the main cause of decay in lime mortars, while in mortars made of gypsum, decay is a result of the solubilizating action of rain wafer.